IB Diploma Biology Practice Test 2026 - Free Biology Exam Practice Questions and Study Guide

The sequence that refers to the events occurring during a heartbeat is known as the cardiac cycle. This term encompasses all the mechanical and electrical events that take place during one complete heartbeat, including the contraction and relaxation of the heart muscles.

During the cardiac cycle, there are specific phases:

1. **Diastole** - when the heart chambers are relaxed and fill with blood.

2. **Systole** - when the heart muscles contract to pump blood out of the chambers.

The cardiac cycle is critical for understanding how blood circulates through the body and how the heart functions to maintain this flow. This includes the sequence of events related to the opening and closing of heart valves, the rhythm and timing of contractions, and the overall efficiency of the heart as a pump. This terminology captures the entirety of the heartbeat sequence, making it the most appropriate choice among the options provided.

In contrast, terms like cardiac interval, cardiac rhythm, and blood flow refer to either specific aspects of heart function or broader cardiovascular concepts instead of describing the comprehensive sequence of events during a heartbeat itself.